As a fuel for internal-combustion engines, diesel fuel ranks second only to gasoline. Further, the importance of diesel as fuel is expected to grow, due to reasons of fuel economy.
A good diesel fuel should meet certain specified requirements. One of the most well known is the cetane index. The cetane index of a diesel fuel is a measure for the ignition quality of a diesel. In general, high cetane fuels eliminate engine roughness or diesel knock, permit an engine to be started at lower air temperatures, provide faster engine warm-up without misfiring or producing white smoke, and reduce the formation of coke deposits. Cetane, which has a high ignition quality represents 100 on the cetane index scale. The cetane index of a fuel depends mainly on its hydrocarbon composition. In general, paraffins have a high cetane index, followed by olefins and cycloparaffins, while aromatics have the lowest cetane index. Another parameter which is of importance for a diesel fuel is its API gravity, which is a measure for the density of fuel. Diesel fuel is sold by volume. The greater the volume swell (density decrease), the greater the increase in product value.
We have now developed a process for the production of a diesel fuel with an improved cetane index and API gravity. In addition, this desired effect is obtained without a substantial increase in hydroconversion activity.